1. Field
Embodiments of the present invention relate to a method of controlling an Anti-lock Brake system (ABS) of an electronic brake, which is driven using an electric motor.
2. Description of the Related Art
An electronic brake to be driven using an electric motor is used to reduce speed of a vehicle or stop the vehicle, or to keep the vehicle stationary. Such an electronic brake conventionally generates brake force by strongly compressing opposite sides of a disc, rotated along with a wheel, using brake pads.
When performing Anti-Lock Brake System (ABS) braking in which braking and braking-release motions are repeated at a rapid period using such an electronic brake, maintaining a vehicular wheel slip value in a band as close to optimal as possible may be necessary to achieve vehicle stability and to reduce stopping distance. Maintaining a vehicular wheel slip value in a band as close to optimal as possible serves to reduce variation of the wheel slip value. To this end, it may be very important to control a position of an electric motor to assure rapid reciprocating movement thereof.
The most basic motor control method in relation to ABS braking is to reciprocate an electric motor between a braking position and a braking-release position according to a change in wheel speed. A variety of known methods may be used to determine the two braking and braking-release positions and to determine reciprocating movement conditions between the two positions. For example, in a method based on a wheel slip value, the electric motor is moved from the braking position to the braking-release position under the condition that wheel locking (i.e. a braking-release section) is determined if the wheel slip value exceeds a predetermined value, whereby brake force is reduced. Also, the electric motor is moved from the braking-release position to the braking position under the condition that reapplication of brake force (i.e. a re-braking section) is determined if the wheel slip value is smaller than the predetermined value, whereby brake force is again generated.
Although rapid implementation of braking and braking-release motions during ABS braking depends on the maximum operating speed of an actuator (e.g., the electric motor and a speed-reduction gear) that is used to move brake pads in the electronic brake, the brake force is inversely proportional to the movement speed of the brake pads and thus, there is a limit to how much the movement speed of the brake pads can be increased. Accordingly, in consideration of the present technology level in relation to the actuator (the electric motor and the speed reduction gear), position control of the brake pads (more particularly, position control of the electric motor) may often be slower than a change in wheel speed. Thus, conventional motor position control methods have difficulty acquisition of excellent ABS control responding performance.